1. Field of the Invention
The invention relates to a method for controlling a packet transmission between a sender and a mobile receiver, and a mobile network element.
2. Description of the Related Art
This invention is related to wireless and packet transport protocols such as TCP (Transport Control Protocol). TCP was designed under the assumption that the end-to-end path of a TCP connection does not change during a session and therefore the congestion control algorithms are triggered solely on packet loss or timeout information. In wireless networks, the user moves from one cell to another, which triggers different types of mobility events (e.g., cell updates or RA (Routing Area) updates). In this connection, it is noted that in packet switched networks (like GPRS (General Packet Radio Service) or EGPRS (Enhanced GPRS)), if the mobile is in data transfer mode and moves out of range of current cell, connection in current cell is terminated and re-established in the new cell. Before re-establishing connection in a new cell, a mobile station in general does a cell reselection and selects a new cell, this new cell may belong to same RA or different RA. If it belongs to same RA, the mobile station will do the cell update otherwise it will do the RA update.
Downlink packets are lost during some types of mobility events. For example, in an EGPRS (also referred to as EDGE (Enhanced Data Rates for GSM Evolution)) network, downlink LLC PDUs (Logical Link Control Packet Data Units) in UNACK mode (i.e., in a mode in which no acknowledgement messages or the like are sent) are lost during Inter-BSC RA (Inter Base Station Controller Routing Area) update or Inter-SGSN (Serving GPRS Support Node) RA update, etc. This leads to the fact that the design assumption of TCP does not holds good in wireless environments.
TCP dynamically calculates the end-to-end network capacity in order to avoid packet loss due to buffer overflow. TCP assumes packet loss in the network as an indication of congestion in the network. This assumption holds good in wire-line network, but in wireless networks, there are events not related to network congestion, which cause data loss. These events include some handoff procedures. When such handoff-induced losses occur, it is anti-optimal to wait for the TCP sender to time-out (as is the case currently with TCP).